IEB 80-17 Supplement 1 Failure of Control Rods to Insert During a Scram at a BWR (Generic Letter 80-66)

GL80066 SSINS No. 6820
Accession No.:
8006190027
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
July 18, 1980
IE Bulletin No. 80-17
Supplement No. 1
FAILURE OF 76 OF 185 CONTROL RODS TO FULLY INSERT DURING A SCRAM AT A BWR
Description of Circumstances:
Please refer to IE Bulletin 80-17, issued July 3, 1980, for complete details
of the initiating event. Although we are essentially confident that the
event was caused by water in the Scram Discharge Volume (SDV) system we do
not yet have a complete explanation as to why the water was present. The
best estimate is that some type of blockage existed in the vent and/or
drainage system for the SDV, precluding adequate drainage. To ensure that
the SDV is empty, Browns Ferry (BF-3) has installed instrumentation to
continuously monitor the water in the scram discharge volume. Such
instrumentation is being considered by other plants.
Since issuance of IE Bulletin 80-17, additional information has been
identified. Specifically:
a) At Browns Ferry a discrepancy was found between the "as-built" scram
discharge system and the "as-designed" system. An unused one-inch (1")
instrument line was found uncapped on the four-inch (4") drain header
on the west side (the side whose rods scrammed) scram discharge volume
vent system of Unit No. 3. It is believed that this line improved the
venting, and therefore the drain time for that system.
b) It has been determined that the vent systems on some scram discharge
volumes interconnect with vent headers that are also common with and
are connected to other systems. The interconnected "vent" system may
contain water drained or being drained from those other systems. This
water could potentially affect performance of the SDV. Also, both the
vent and drain systems for the scram discharge system may contain long
lengths of relatively small bore piping. Designs specify a very
gradual slope, such that small errors in the "as-installed" piping
could result in degraded performance (for example, due to loop seals).
c) Concerns have been expressed within the NRC Staff regarding potential
delays that may occur before start of injection of boron into the BWR
system from the Standby Liquid Control System (SLCS) when this manual
operator action is required. The potential delays could be caused by
unavailability of the SLCS key which is required to initiate this
system, and/or administrative delays which require supervisory approval
before the SLCS can be manually initiated by the control room licensed
operator.
In view of the above items, the following actions in addition to those
specified in IE Bulletin 80-17 are to be taken by BWR licensees.
.
A. Action to be Taken by BWR Licensees Upon Receipt and to be Reported
Within 20 Days of the Date of This Letter:
1) Provide to the NRC Regional Office an analysis of the adequacy of
the "as-built" SDV system and associated vent and drain systems,
including any identified design deficiencies. Include copies of
verified "as-built" isometric drawings of the SDV and detailed
descriptions of the system, verified to be correct, as part of
this analysis.
2) Revise and implement Operating Procedures as necessary to provide
clear guidance to the licensed operator in the control room
regarding when he should initiate the SLCS without obtaining prior
supervisory approval. Provide a description of the implemented
procedural requirements.
3) Assure that procedures exist and are implemented for specifying
remedial action to be taken if water is found in the SDV system at
times when it should be free of water. Provide a description of
the implemented procedural requirements.
4) Revise and implement administrative procedures as necessary to
ensure that the SLCS key shall be readily available to the
licensed operator in the control room. Provide a description of
the implemented procedural requirements.
5) Continue daily monitoring of water levels in all scram discharge
volumes until continuous monitoring system(s) (discussed in B.1
below) is (are) installed and operational (this requirement
supersedes the requirements of Item 5 of IE Bulletin 80-17 which
required daily surveillance for only 6 days).
B. Action to be Taken by BWR Licensees and Completed by September 1, 1980:
1) Install a system to continuously monitor water levels in all scram
discharge volumes. Continuous recording and alarm features must
be included in the design. Consideration should be given to use
of diverse level sensors in this (these) system(s). The design
installed should represent the design with the highest level of
reliability compatible with completion of installation by
September 1, 1980. Provide a written description of the system
design to the NRC Regional Office.
If installation by September 1, 1980 is not possible, by August
15, 1980, submit to the NRC Regional Office:
1) Documentation in detail why the installation cannot be
completed by 9/1/80.
2) A Commitment to a firm schedule for installation.
3) A commitment to equipment changes and/or surveillance
requirements in addition to those now in effect that will
provide adequate assurance of SDV operability in the interim
until installation is completed.
.
2) Perform a study of potential designs for improving the venting
system for the scram discharge volumes and submit a description to
NRC by September 1, 1980. Improvements such as providing a
redundant, independent vent for each significant volume in the
system or locally installed vacuum breakers close to each such
volume should be considered (some plants already include a design
which vents locally to atmosphere). Include an estimate of the
time that would be required to accomplish these modifications in
your report to be submitted to the NRC Regional Office. We have
been told that meetings have already been scheduled by GE to
discuss their proposals in this area with licensees.
Additional requirements are under consideration and will be the subject of
further communication from NRC.
Licensees of all operating BWRs shall submit the information requested
within the specified allowable times. This information is requested under
the provisions of 10 CFR 50.54 (f). Accordingly, you are requested to
provide within the time periods specified above, written statements of the
above information signed under oath or affirmation. Reports shall be
submitted to the Director, Division of Reactor Operation Inspection, NRC.
Office of Inspection and Enforcement, Washington DC 20555.
Approved by GAO, B180225 (R0071); clearance expires 7-31-80. Approval was
given under a blanket clearance specifically for identified generic
problems.